High temperature treatment of lignocellulosic material, such as wood, makes it possible to reduce their moisture content and improve their stability characteristics.
Various methods and apparatus for carrying out high temperature treatment of lignocellulosic materials are known. FR-A-2,720,969 discloses such a method and a cell for carrying it out. This document discloses drying of the materials, followed by heating in a closed circuit during which the gases released by the material are employed as a fuel, and finally, cooling by injection of water. The closed-circuit heating step disclosed in this document does not make it possible to ensure residual humidity, remaining after the drying step, is completely eliminated. Additionally, the use of the gases released by the material as a fuel involves control of the treatment plant which is difficult to achieve in practice. Finally, injecting water for cooling leads to the material treated splitting or breaking up. The cell disclosed in that document for carrying out the method has corresponding disadvantages, and in practice, it is difficult or even impossible to carry out material treatment inside it. In particular, it is difficult, with this apparatus, to ensure that the gases released are subject to combustion, as proposed in the method, and it is also difficult and dangerous to carry out heating in a closed circuit. U.S. Pat. No. 6,374,513 discloses an apparatus and a method for high temperature disclosure in which delivery channels carry the gases to the treatment chamber on one side, and an induction channel, on the other side of the treatment chamber, recovers the gases to be channeled to a combustion chamber. However, the arrangement of this apparatus, which is further described below, creates a unidirectional flow of gas within the treatment chamber that results in temperature inhomogeneity within the material being treated. While this has utility in certain circumstances, there is a need for an improved apparatus for treating lignocellulosic material.